Living organisms are protected from foreign substances mainly by immune responses, and the immune system is made up of various cells and soluble factors produced by them. Among them, a white blood cell, in particular, a lymphocyte plays a central role. The lymphocyte is divided into two major types, B lymphocyte (hereinafter referred to as B-cell) and T lymphocyte (hereinafter referred to as T cell), both of which recognize antigens specifically and act on them to defend the organism.
In the peripheral blood, the majority of T cells are occupied by CD (Cluster of Differentiation) 4-positive T cells having a CD4 marker and CD8-positive T cells having a CD8 marker. The majority of the CD4-positive T cells are called helper T cells (hereinafter referred to as Th cell), which are involved in assistance of antibody production and induction of various immune responses and are classified into Th1 type (Type 1 helper T cell: hereinafter referred to as Th1-type cell) and Th2 type (Type 2 helper T cell: hereinafter referred to as Th2-type cell) depending on different kinds of cytokines produced by antigen stimulation. The majority of CD8-positive T cells are cytotoxic T cells (cytotoxic T-lymphocytes, hereinafter also referred to as CTL) which exhibit cytotoxic activity in response to antigen stimulation.
As the fourth cancer therapy following surgical operations, chemotherapies and radiation therapies, immunotherapies have been recently attracting attention. Since immunotherapies utilize the immunological capability originally possessed by a human, it is said that physical stress on patients is mild as compared with other therapies. Known immunotherapies include therapies comprising transfer of cells such as lymphokine-activated cells, CD4-positive T cells, NKT cells or γδT cells which are obtained by expansion from CTLs induced ex vivo, a peripheral blood mononuclear cell or the like according to various methods; dendritic cell-transferring therapies and peptide vaccine therapies by which induction of an antigen-specific CTL in vivo is expected; Th1-type cell therapies; and an immunological gene therapies comprising transducing genes that can be expected to have various effects into the above-described cells ex vivo and transferring the cells into the body, and the like.
In the immunotherapy, cell therapy using CTLs which have cytotoxic activity has been traditionally provided. However, recently, Th-cell therapy using Th cells which assist the activity of the CTLs attracts attention (for example, Non-patent Literature 1, Patent Literature 1). As described above, Th cells are classified into Th1-type cells and Th2-type cells. The Th1-type cells produce cytokines such as interferon-γ (IFN-γ) and interleukin-2 (IL-2) and serve as an effector of cellular immunity. On the other hand, the Th2-type cells produce cytokines such as IL-4, IL-5, and IL-13 and have a role in regulation of humoral immunity.
As a cell therapy for acquired immune deficiency syndrome (AIDS), a therapy comprising modifying a CD4-positive T cell (for example, by gene transduction) which is the target of HIV viruses, and then transferring the modified cell into a patient recently attracts attention (for example, Non-patent Literature 2). For example, a clinical trial is conducted in the United State wherein the CD4-positive T cell of an HIV patient is transduced with a gene expressing an antisense RNA corresponding to an RNA encoding gp120 which is a structural protein for HIV, and then the CD4-positive T cell having the added anti-HIV effect is transferred into the patient.
In recent years, a naive T cell and a central memory T cell which are in more undifferentiated states attract more attention rather than a Th cell which is a terminally differentiated effector. The naive T cell is a cell (Th0) which has never been activated by an antigen and has not been directed toward differentiation into a Th1-type cell or a Th2-type cell. It has been shown that the differentiation of the naive T cell into a Th1-type cell or a Th2-type cell can be induced by culturing a CD4-positive naive T cell in the presence of an antigen and a cytokine. The naive T cell is known to express cell surface antigen markers of lymphocytes such as CD45RA, CD62L, and CCR7.
As described above, the naive T cell in an undifferentiated stage is important in the fields of cell therapy and gene therapy. For production of a cell population, development of a method comprising a step of producing with high cell growth efficiency a large amount of cells suitable to use in therapy is desired, and thus, a method of producing a Th1-type cell is developed (for example, Patent Literature 2).